Coursehero >> California >> Presidio School of Management >> ECS 153

Course Hero has millions of student submitted documents similar to the one below including study guides, homework solutions, papers, exam answer keys and textbook solutions.

2 HOMEWORK ECS 153 FALL 2000 Homework 2 Due Date: November 2, 2000 1. 2. 3. (20 points) Chapter 14, exercise 6 (20 points) Chapter 14, exercise 9 (160 points) This exercise asks you to determine how the various shells access environment variables, and test for a potential problem. a. Write a program called envalter to add environment variables to an environment and then spawn a subprogram. Your program should take the following arguments: b env add the environment variable env to the beginning of the environment. Env may be an environment variable name or a name and value (var or var=value, respectively). d env delete all occurrences of the environment variable env from the environment. If env is an environment variable name, delete all environment variables with that name. If env is a name and value, delete only those variables with the given name and value. e env like b, except the environment variable env is added to the end of the environment. program execute the program in the new environment Hint: use execve(2) to execute the program. Do not use system(3)! Write a second program called shell that determines whether a given shell uses the rst or last search path in the environment. This program should take the arguments: following f dir put the rst xyzzy program in this directory (if not given, use the directory xyzzy1) l dir put the second xyzzy program in this directory (if not given, use the directory xyzzy2) shell use the named shell Hint: Create two programs called xyzzy. One should print it s the rst and the other it s the last . Use the program you wrote in part a to delete the current search path, and add two new search paths. The rst adds a search path containing the directory with the rst xyzzy to the front of the environment, and the second adds a search path containing the directory with the second xyzzy to the end of the environment. Then spawn a shell and see which program is executed. Bundle your programs into a distribution mechanism that works as follows. After un-taring the program, the recipient types make to compile (set up) both programs. The recipient can then type ./check shell where shell is the name of a shell (either relative or full path name) and the program will print: one of: shell: uses the rst occurrence of the environment variable shell: uses the last occurrence of the environment variable 200 Points b. c. Version of October 26, 2000 11:02 am Page 1 of 1

Find millions of documents here - Study Guides, Homework Solutions, Papers, Exam Answer Keys and more. Course Hero has millions of course related materials that will enable you to learn better, faster and get an A in all your courses.
Below is a small sample set of documents: